1. Field of the Invention
The present invention relates to methods and apparatus for supplying dissolved gases (such as oxygen, ozone, chlorine, etc.) for chemical and biological processes. The methods and apparatus of the present invention are particularly suitable for use in the biodegradation of organic matter (such as in municipal and industrial wastewater treatment), the oxidation and precipitation of dissolved metals, the oxidation and destruction of dissolved organic contaminants in wastewater, the farming of aquatic species (such as fish and shrimp), the control of odors (such as those caused by anaerobic bacteria in contaminated wastewater or sludge), and the killing of bacteria in potable water and in water to be discharged into public streams.
2. Description of Related Art
Municipal wastewater treatment plants may require aeration of the wastewater under treatment for the entire duration of the biological treatment process, consuming large amounts of dissolved oxygen. The oxygen is typically introduced into the process by bubbling air through the wastewater under treatment with a small percentage of oxygen actually being dissolved or transferred to the liquid state and available to the mass of microorganism in performing its function. The aeration or oxygen transfer efficiency at its best is very low with the aeration process perhaps consuming as much as 50 to 90 percent (50% to 90%) of the total energy costs of a typical municipal treatment facility.
The control of the aeration process is typically based on the amount of excess dissolved oxygen over what was consumed in the biodegradation process that is left in the wastewater to be discharged to public streams after treatment. When the excess dissolved oxygen reaches a predetermined low level in the treated wastewater to be discharge, additional air is bubbled through the wastewater under treatment until the dissolved oxygen is again within an acceptable range in the treated wastewater to be discharged from the process and presumed to be sufficient in the treatment process.
A certain amount of excess oxygen is desirable as protection against any temporary increase in oxygen demand. However, any amount of excess oxygen taken out of the process with the wastewater that has completed treatment adds significantly to the costs of the treatment process because of the low oxygen transfer efficiency in the aeration process. Because of the high-energy costs of aeration, the amount of dissolved oxygen may be maintained at levels below what might be used for optimum biodegradation processes.
In reviewing any process requiring oxygen dissolved in a liquid, like in water or wastewater, the primary issue soon becomes the high costs of energy associated with the inefficiency of transferring the oxygen to a dissolved state in the water to be available for the process.
With the present state of technology available, the costs are minimized by maintaining the minimum amount of dissolved oxygen in the process needed to perform the biological destruction of contaminants, keeping the contaminated wastewater in the treating process for a minimum amount of time, and keeping the excess oxygen allowed to be discharged with the treated wastewater at a minimum, again because of the high costs of energy associated with dissolving oxygen in the wastewater related to the low oxygen transfer efficiency.
In addition to supplying dissolved oxygen from biological processes, oxygen (O2) from air, pure oxygen (O2), ozone (O3), chlorine (Cl2), hydrogen peroxide (H2O2), and potassium permanganate (KMnO2) are examples of the oxidants available for treating wastewater and react directly in chemical oxidation-reduction reactions with many contaminants so they can be removed in order to comply with the regulatory requirements for discharge of the water into streams or prevent discharge of the volatile contaminants into the atmosphere. The oxidants can also be used to remove contaminants as bacteria, iron, hydrogen sulfide, manganese, pesticides, and others from water to make it potable. In order to perform their function the oxidants must first be dissolved in the water or wastewater in which the chemical oxidation-reduction reactions are to occur. The same low efficiencies of bubbling air through the water or wastewater are realized in many direct chemical oxidation-reduction reactions as they are in biological degradation processes.
With respect to the present invention, the methods and apparatus will, for convenience, be discussed in terms of supplying dissolved oxygen and ozone for use in the treatment of contaminated water and wastewater to support biological and chemical oxidation-reduction reaction processes. It should be clearly understood, however, that the methods and apparatus of the present invention might be used in the treatment of many other fluid solutions with either oxidizing or reducing agents regardless of their intended use or how they become contaminated.
An apparatus and method capable of dissolving oxygen with a much higher efficiency than currently available, if generally applied, may greatly reduce the energy consumption of the United States and other nations in their sewage treatment plants. The present invention overcomes the deficiencies of previous methods and apparatus by dissolving high concentrations of oxygen, and other gases, in an enclosed and pressurized apparatus exposing the mass of microorganisms and contaminants to the high level of dissolved oxygen inside the apparatus and then injecting the fluid concentrated with oxygen into the general treating process and exposing the rest of the mass of microorganisms and contaminants to higher oxygen levels than what is capable of being reached by bubbling air through the treating process based on Henry's Law.
Also, a second embodiment of the apparatus of the present invention is capable of dissolving all oxygen gases into the fluid (such as water and wastewater) without discharging any to the atmosphere, making it economically feasible to use technically pure oxygen separated from air to increase the concentration of oxygen even further to a level in excess of four times the level that can be reached by using air that is only approximately twenty percent (20%) oxygen. The use of technically pure oxygen allows the reduction of the size of the apparatus to approximately one-fourth of the size required for dissolved air with twenty percent oxygen with an associated reduction in energy consumption.